Final answer:
The allele combinations on one axis of a dihybrid cross for a parent with the genotype XxYY would be XY and xY, reflecting the possible gametes this parent can produce.
Step-by-step explanation:
The student asked about the allele combinations for a dihybrid cross for a parent with the genotype XxYY. In a dihybrid cross, you look at two separate traits, which are determined by two distinct gene pairs. Since the parent in question has the genotype XxYY, we must consider both the Xx and the YY parts of the genotype. For the Xx part, there are two possible alleles that can be passed on: X or x. However, for the YY part, because the parent is homozygous dominant, the only allele that can be passed on is Y. As such, the alleles on one axis of a Punnett square would be XY and xY, representing the combination of alleles from this parent's genotype that can be passed to the offspring.